Audio equalization filters are used in a variety of audio signal processing systems to modify an audio signal so that the transfer function of the system conforms to a desired frequency response. For example, an equalization filter may be used to compensate for frequency-response characteristics of electronic and acoustic components of an audio playback system so that the overall system transfer function is spectrally flat.
The frequency response of an equalization filter may be static or dynamic; however, dynamic or adaptive equalization (AEQ) filters are preferred for many applications because they can compensate for changing response characteristics of a system. Traditional AEQ filters operate by minimizing a measure of difference between two time-domain signals such as system input and output signals, and they are responsive to both magnitude and phase differences between the signals.
These traditional AEQ filters, whether static or dynamic, typically require an initial setup or calibration process to determine system response characteristics for both magnitude and phase so that the values of one or more parameters of the equalization filter can be set properly. For example, an initial setup process is typically required to determine a variety of characteristics very accurately such as equipment signal processing delays and acoustic signal propagation delays so that phase errors due to temporal misalignment can be minimized. If the initial setup process is not done properly, temporal alignment errors may cause an conventional AEQ filter to operate poorly and become unstable under certain conditions.